This invention relates generally to nanotubes, and more particularly relates to nanopore-based devices that incorporate nanotubes.
Nanopore-based devices have become important for a wide range of applications including detection, analysis, and quantification of species on the nanoscale. Nanopores are generally considered to be apertures having a diameter on the nanoscale. Many nanopore-based structures are being developed specifically for applications related to molecular sensing. For example, it has been suggested to translocate a molecule provided in an ionic solution, such as a strand of DNA, through a nanopore in a solid-state membrane, and to measure the blockage of ionic current through the nanopore as the molecule translocates through the nanopore.
It has been demonstrated that a characteristic blockage of the ionic solution, and the corresponding ionic current, through a nanopore can be attributed to a corresponding translocating molecule. But although molecule-specific ionic current blockage has been demonstrated, it has been found that the small differences in ionic current blockage corresponding to translocation of molecular components, such as different DNA bases, are generally beyond the resolution limit of conventional current amplifiers because, e.g., the intrinsic noise due to the electrically charged DNA bases is so large. It therefore is not in general currently possible to discriminate between specific DNA bases solely by measurement of ionic current blockage through a nanopore.
To overcome this limitation in discrimination between distinct translocating species, it has been proposed to alternatively, or to in addition, employ an electronic sensing arrangement, or electronic sensor, such as a tunneling junction, at the site of a nanopore, for electronically sensing molecules translocating through the nanopore. In one proposed configuration, there is provided one or more electrodes at the site of a nanopore to measure an electrical signal parameter indicative of molecular interaction with the nanopore. For example, a measurement can be made of transverse electronic current across a molecule translocating through a nanopore. This measurement technique is motivated by an analogy with scanning electron microscopy (STM) experiments, in which individual DNA bases are known to produce distinct electronic tunneling signals.
Theoretical calculations of a coupling interaction between a DNA molecule and embedded electrodes at the site of a nanopore have predicted orders of magnitude differences between the electronic tunneling currents corresponding to the four different DNA bases. To achieve such enhanced tunneling current sensing, it has been proposed to employ one or more carbon nanotubes as electrodes provided at the site of a nanopore. The unique electronic structure, exceptional elastic properties, and extremely high aspect ratio all characteristic of carbon nanotubes address many considerations for successfully implementing nanoscale electrodes at the site of a nanopore.